This invention relates to a connector assembly which provides strain relief and shielding for a flat shielded braided cable.
The rise of miniaturization in the electronic industry placed a large number of discrete signal-receiving devices, e.g., integrated circuit chips, in tiny areas. The diameters of the signal-carrying wires were small enough taken alone, but the number required to connect a printed circuit board having a number of these devices thereon, created a bulky package. Flat cable consisting of numerous conductors surrounded by a single dielectric sheath provided an initial answer. Flat cable allows high density wiring, offers a neat appearance, and is conducive to use with labor-saving mass termination insulation displacement connectors. The use of flat cables for interconnecting components of electrical and electronic equipment has rapidly increased.
The increased utilization of such cable however, caused a resulting problem of electromagnetic interference (EMI) which results in the unintended transfer and obstruction of electronic signals. This phenomenon forced workers in the field to seek an improved cable. An early effort to eliminate EMI resulted in a ribbon cable having a shield wrapped around, it, such as that disclosed in U.S. Pat. No. 3,634,782 Marshall. Subsequently, U.S. Pat. No. 3,663,739 Chevrier issued, which taught wrapping a shield around each wire, i.e., around the dielectric surrounding each center conductor. Cross-talk between individual conductors, as well as interference to and from the ribbon, was effectively prevented. With the proliferation of computer equipment and the increased frequencies or pulse rates employed in such equipment, the problem of controlling electromagnetic interference (EMI) has resulted in the FCC and other similar authorities imposing increasingly stringent shielding requirements.
The solving of the EMI problem, however, brought about the problem of terminating the shielding from the cable to the connector. The shields in most common usage consist of a film, such as Mylar.RTM. with a conductive material. These kinds of shields prohibit all but the very careful stripping of the outer insulating jacket.
One feature provided by many prior art connector housings is strain relief at the point where the cable enters the connector housing. Often strain relief is provided by a complex collar and clamp mechanism attached to the housing. One disadvantage of some commonly available clamps is that they tend to squash the cable rather than clamping it uniformly about its periphery. Several prior art disclosures, such as U.S. Pat. Nos. 4,534,608, 4,458,967 William et al, 4,537,458 Worth provide strain relief in this manner U.S. Pat. No. 4,534,608 Scott et al specifically teaches strain relief through a series of ribbed ridges which deform the cable into a "serpentine" configuration.
U.S. Pat. Nos. 4,040,705, Huber and 4,040,704 Huber illustrate a second related problem with the prior art the breaking or piercing of the dielectric outer shell in order to secure clamping and strain relief.
The methods disclosed by the prior art also rely on the resiliency of the outer dielectric insulating jacket to maintain firm contact between the connector housing and cable in order to facilitate strain relief. With age, the plastic material of the outer dielectric shell loses its resiliency and takes a permanent set. Inadequate tightening results in poor electrical contact and strain relief, while excessive tightening of the blocks beyond the elastic limits of the jacket material and the outer insulation could result in short-circuiting of the conductors.
A final problem with the prior art connectors, is that they were designed to accommodate only one specific cable or line of products.
The present invention successfully solves the problems associated with these prior art connectors. In accordance with the invention, a connector firmly and uniformly connects a flat shielded braided cable, simultaneously providing electromagnetic shielding and strain relief for a variety of cable sizes and diameters. It eliminates the need of breaking the outer dielectric shell, and solves the problems of poor contact due to lack of resiliency. Finally, it provides strain relief without squashing or in any way impairing the multi-conductor cable or the shielding.